bind-wrapper.c

/*	Copyright 2015-2023 Rivoreo

	Permission is hereby granted, free of charge, to any person obtaining
	a copy of this software and associated documentation files (the
	"Software"), to deal in the Software without restriction, including
	without limitation the rights to use, copy, modify, merge, publish,
	distribute, sublicense, and/or sell copies of the Software, and to
	permit persons to whom the Software is furnished to do so, subject to
	the following conditions:

	The above copyright notice and this permission notice shall be
	included in all copies or substantial portions of the Software.

	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
	EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
	MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
	NONINFRINGEMENT. IN NO EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE
	FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
	CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
	WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

#include <arpa/inet.h>
#include <sys/wait.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netipx/ipx.h>
#include <fcntl.h>
#include <dlfcn.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>

#ifndef LIBC_PATH
// Default to a common GNU/Linux i386 path
#define LIBC_PATH "/lib/libc.so.6"
#warning "You may need to define macro LIBC_PATH"
#endif

#ifndef LIBC_ERRNO_FUNCTION_NAME
#define LIBC_ERRNO_FUNCTION_NAME "__errno_location"
#endif

static void *get_libc() {
	static void *libc;
	if(!libc) libc = dlopen(LIBC_PATH, RTLD_LAZY);
	return libc;
}

static int (*get_libc_bind())(int, const struct sockaddr *, socklen_t) {
	static int (*f)(int, const struct sockaddr *, socklen_t);
	if(f) return f;
	void *libc = get_libc();
	if(!libc) {
		perror("dlopen");
		abort();
	}
	*(void **)&f = dlsym(libc, "bind");
	if(!f) {
		perror("dlsym: bind");
		abort();
	}
	return f;
}

static int *get_libc_errno() {
	static int *(*f)(void);
	if(f) return f();
	void *libc = get_libc();
	if(!libc) {
		perror("dlopen");
		abort();
	}
	*(void **)&f = dlsym(libc, LIBC_ERRNO_FUNCTION_NAME);
	if(!f) {
		perror("dlsym: " LIBC_ERRNO_FUNCTION_NAME);
		abort();
	}
	return f();
}

#ifdef __linux__
// Return boolean
static int bind_to_device_via_external_helper(int fd, const char *interface) {
	pid_t pid = fork();
	if(pid < 0) {
		perror("fork");
		return 0;
	}
	if(pid) {
		int status;
		while(waitpid(pid, &status, 0) < 0) {
			if(errno == EINTR) continue;
			if(errno == ECHILD) return 1;	// Why?
			perror("waitpid");
			return 0;
		}
		return status == 0;
	} else {
		char fd_s[10];
		snprintf(fd_s, sizeof fd_s, "%d", fd);
#ifdef BIND_TO_DEVICE_HELPER_PROGRAM_PATH
		execl(BIND_TO_DEVICE_HELPER_PROGRAM_PATH, BIND_TO_DEVICE_HELPER_PROGRAM_PATH,
#else
		execlp("bind-socket-to-device", "bind-socket-to-device",
#endif
			fd_s, interface, (char *)NULL);
#ifdef BIND_TO_DEVICE_HELPER_PROGRAM_PATH
		perror(BIND_TO_DEVICE_HELPER_PROGRAM_PATH);
#else
		perror("bind-socket-to-device");
#endif
		_exit(127);
	}
}
#endif

int bind(int fd, const struct sockaddr *addr, socklen_t addr_len) {
	fprintf(stderr, "function: bind(%d, %p<sa_family=%hu>, %u)\n",
		fd, addr, addr ? addr->sa_family : -1, (unsigned int)addr_len);
	int r = get_libc_bind()(fd, addr, addr_len);
	int e = r < 0 ? *get_libc_errno() : 0;
#ifdef __linux__
	if(r == 0 && addr->sa_family == AF_INET) {
		const struct sockaddr_in *insa = (const struct sockaddr_in *)addr;
		if(!insa->sin_addr.s_addr) {
			unsigned int port = ntohs(insa->sin_port);
			fprintf(stderr, "Socket %d bound to *:%u\n", fd, port);
			if(port == 5000 || (port & 0x40) == 0x40) {
				fputs("IPX wrapper guessed\n", stderr);
				const char *bind_interface = getenv("BIND_INTERFACE");
				if(bind_interface && *bind_interface) {
					fprintf(stderr, "Binding socket %d to '%s'\n", fd, bind_interface);
					if(setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, bind_interface, strlen(bind_interface)) < 0) {
						perror("setsockopt: SO_BINDTODEVICE");
						fputs("Trying external helper program\n", stderr);
						if(!bind_to_device_via_external_helper(fd, bind_interface)) {
							fputs("Failed\n", stderr);
						}
					}
				}
			}
		}
	} else
#endif
	if(r < 0 && e == EACCES && addr->sa_family == AF_IPX) {
		const struct sockaddr_ipx *ipxsa = (const struct sockaddr_ipx *)addr;
		uint16_t port = ntohs(ipxsa->sipx_port);
		unsigned char network_number[4];
#ifdef __linux__
		memcpy(network_number, &ipxsa->sipx_network, 4);
#else
#define network_number ((struct sockaddr_ipx *)&ifr->ifr_addr)->sipx_addr.x_net.c_net
#define sipx_node sipx_addr.x_host.c_host
#endif
		pid_t pid = fork();
		if(pid < 0) {
			perror("fork");
		} else if(pid) {
			int status;
			while(waitpid(pid, &status, 0) < 0) {
				if(errno == EINTR) continue;
				if(errno == ECHILD) return 1;	// Why?
				perror("waitpid");
				return 0;
			}
			if(status == 0) r = 0;
		} else {
			char fd_s[10], network_s[12], node_s[18], port_s[6];
			snprintf(fd_s, sizeof fd_s, "%d", fd);
			snprintf(network_s, sizeof network_s, "%02hhx:%02hhx:%02hhx:%02hhx",
				network_number[0], network_number[1], network_number[2], network_number[3]);
			snprintf(node_s, sizeof node_s, "%02hhx:%02hhx:%02hhx:%02hhx:%02hhx:%02hhx",
				ipxsa->sipx_node[0], ipxsa->sipx_node[1], ipxsa->sipx_node[2], ipxsa->sipx_node[3], ipxsa->sipx_node[4], ipxsa->sipx_node[5]);
			snprintf(port_s, sizeof port_s, "%u", (unsigned int)port);
#ifdef IPXBIND_HELPER_PROGRAM_PATH
			execl(IPXBIND_HELPER_PROGRAM_PATH, IPXBIND_HELPER_PROGRAM_PATH,
#else
			execlp("ipxbind", "ipxbind",
#endif
				fd_s, network_s, node_s, port_s, (char *)NULL);
#ifdef IPXBIND_HELPER_PROGRAM_PATH
			perror(IPXBIND_HELPER_PROGRAM_PATH);
#else
			perror("ipxbind");
#endif
			_exit(127);
		}
	}
	if(r < 0) errno = e;
	return r;
}